15% reduction in calories slowed aging and metabolishm. 53 non-obese humans between 21 and 50 cut calories for two years. Calories reduction was monitored with the ratio of isotopes absorbed. No adverse effects found. Mood and health QoL improved.

"...found that even people who are already healthy and lean may benefit from a calorie restriction regimen,"

support for two of the longest-standing theories of human aging: the slow metabolism 'rate of living' theory and the oxidative damage theory